It is desirable to monitor the condition of tires as to wear, internal temperature and internal pressure. It is particularly advantageous to monitor large truck tires since these are expensive and must be regularly maintained to maximize vehicle efficiency.
In the past, such monitoring activities have generally used a passive integrated circuit embedded within the body of the tire and activated by a radio frequency transmission which energizes the circuit by inductive magnetic coupling. Passive devices which rely on inductive magnetic coupling or capacitive coupling generally have the disadvantage of requiring lengthy coil windings, thus requiring major modifications in the tire construction and assembly process. Another serious disadvantage with such passive devices is that the interrogator must be positioned in very close proximity to the tire, usually within a few inches of the tire, in order to allow communication between the tire and the device. Because of the proximity requirements, continuous monitoring is impractical since it would require that an interrogator be mounted at each wheel of the vehicle. Manual acquisition of data from the passive devices embedded in each of the tires of a parked vehicle is also cumbersome and time consuming because of the proximity requirements.
Other prior art devices used for monitoring tire conditions have comprised self-powered circuits which are positioned external of the tire, such as at the valve stem. Externally mounted devices have the disadvantage of being exposed to damage, such as from weather and vandalism. Another disadvantage with installing devices external of the tire is that the device itself introduces additional sealed joints from which air may leak. Additionally, externally installed devices can easily become disassociated from a particular tire which is being monitored.
Another disadvantage with known tire monitoring and identification devices is that communication transmissions are achieved using conventional radio frequencies which generally require a relatively large antenna which must be mounted externally or secured to the tire in such a manner which requires relatively major modifications in the tire construction or assembly process.